准噶尔盆地的磁性基底

本文通过分析和反演航磁异常场,研究了准噶尔盆地的磁性基底。分离异常是反演的前提。盆地区域磁场变化幅度很大,它几乎淹没了其他类型的异常。由于用功率谱极值点和矩谱法估算的磁性地壳底面深度相近,为确定区域场提供了有力的佐证。应用矩谱法和辅以正演模拟,了解基底局部埋深和获得可视作均匀磁化的依据,得以用Hahn的方法作反演。反演给出的盆地磁性基底起伏与浅地表大断裂对应很好。它揭示出受盆地形状影响,在南北向压应力作用下,以断裂活动为主,该基底形成了由三岔形隆起带分割成三个构造区。结合地质、遥感、重力资料分析表明;该基底磁性强,密度高,物性均一,属于刚硬的古老结晶基底。受基底控制,不仅盆地上部长期稳定,而且在北疆地史演化中它起了构造砥柱的作用。

THE MAGNETIC BASEMENT OF THE JUNGGAR BASIN

Abstract Through analysis and inversion of the aeromagnetic anomaly field, this paper has studied the magnetic basement of the Junggar basin. The separation of anomalies is the pre-requisite of the inversion- The regional magnetic field in the basin varies considerably and almost covers all other types of anomalies. The bottom of the magnetic crust estimated by the extreme points of power spectra is close to that estimated by the matrix spectrum method in depth, and this convincingly provides evidence for the determination of the regional field. Using the matrix spectrum method with the help of forward simulation, one can understand the local buried depth of the basement and obtain the basis which might be regarded as homogeneous magnetization so as to make inversion with Hahn's method. The relief of the magnetic basement of the basin shown by the inversion is quite consistent with the near-surface great fault. It is revealed that, due to the influence of the shape of the basin, faulting was dominant under the action of the north-south compressive stress and, as a result, this basement was divided into three tectonic units by a fork-shaped uplifted zone. The above studies combined with the geological, remote sensing and gravitational data analysis show that the basement is characterized by strong magnetism, high density and u ifrom physical property, belonging to the rigid old crystalline basement. Controlled by the basement, the basin not only remained stable in the upper part for a long period, but played the role of main tectonic stay in the geological evolution of Northern Xinjiang.